Types of Teeth - Human Teeth Types of Teeth - Human Teeth The 4 Types of Human Teeth Humans, same as the rest of the mammals, are heterodont animals, meaning that they have several different forms of teeth. Human teeth differentiate in shape, while more primitive animals are homodont and all their teeth have the same shape possibly differing only on size. Permanent human teeth come in four different types: incisors , canines , premolars , and molars . Types of teeth Human teeth belong to four distinct types each having a typical appearance and performing a certain function. The shape and morphology of each human tooth type depends on the function that it is assigned to perform. As a species, humans are omnivorous eating both meats and plants, so they need different types of teeth to handle both types of food. Generally, carnivorous animals need sharp teeth to pierce and tear meat, while herbivorous animals need flat teeth to crush and grind plants. Humans, as omnivorous, must have at least these 2 types of teeth. Through evolution humans have developed 4 different main teeth types: 1. Incisors Incisors (Cutting teeth) are the teeth at the center of the dental arch.

There are eight incisors in total in the permanent (and primary) dentition, two on either side (left and right) in the upper and lower jaw. The middle four of them (one at each quadrant) are called central incisors, while the other four next to them are named lateral incisors. Incisors are flat and board, shaped like a shovel with a narrow straight cutting edge that enables them to cut food. The main functions of an incisor in the mastication process are biting, cutting of food into chewable pieces and moving it inwards the mouth. All eight incisors have a single root and almost the same shape, but their size may differ slightly with the upper incisors usually larger, and especially the central ones. 2. Canines (cuspids) Canines (also called eye teeth or cuspids) are the teeth located next to the incisors towards the edge of the mouth. There are 4 canines in both primary and permanent human dentitions, one at each quadrant of the mouth. They are the third teeth from the center. They have a sharp pointed edge that is used to rip and tear tough foods such as meat.

In humans canine teeth have the same height as the rest of the teeth but in other animals they are longer and used to bite and kill prey. Canines have a single but long root that can reach up to 3 cm providing the stability required for their function. They are the longest and most stable human teeth. 3. Premolars (bicuspids) Premolars (also called bicuspids) are the teeth located after the canines towards the back of the mouth. There are eight premolars in the permanent dentition, two on either side (left and right) in the upper and lower jaw. The front four of them (one at each quadrant) are called first premolars, while the other four on the back are called second premolars. The premolars are the fourth and fifth teeth from the midline. Premolars are only present in the permanent dentition; there are no premolars in the primary human dentition. When they erupt, they replace the primary molars. The morphology of premolars is a combination between canines and molars. They are also known as bicuspids, because usually they have at least two cusps on their upper side.

Premolars have a broader surface for chewing and grinding, but they also have some sharp points for piercing and ripping at the edge of the cusps. Their major role is to begin the crushing of foods before they are transferred to the molars for the final grinding. The upper jaw first premolars have two roots, while the upper second ones and all the lower jaw premolars have only one root. 4. Molars Molars are the teeth located at the back of the dental arch. Adult humans have twelve molars, three on either side (left and right) in the upper and lower jaw. There are only 8 molars in the primary dentition which are replaced by the permanent premolars. Permanent molars are named as first, second, and third starting from the front to the back. The third molars are also known as wisdom teeth. Wisdom teeth are the last teeth to erupt behind all other teeth at the age of 17-25 years, much later than the rest. The molars are the sixth, seventh, and eighth teeth from the midline. Molars perform most of the chewing, by crushing and finalizing grinding before swallowing the food.

The first and second molars have a similar shape with premolars, but they are larger (with the first molar larger than the second one). The mandibular first molars (the one at the lower jaw) are usually the largest teeth of the human mouth. They have a more flattened surface with four to five cusps, and two to three roots. The morphology and size of third molars (wisdom teeth) may vary significantly but they are usually smaller than the other molars. In some cases they fail to erupt properly in the mouth, either remaining trapped inside the jaw bone (impacted wisdom teeth), or erupting partially causing a painful condition known as pericoronitis . The Four Types of Teeth and How They Function | Everyday Health Dental Health The Four Types of Teeth and How They Function Your teeth and the structure of your mouth play important roles in your ability to eat and speak and stay healthy. Sign Up for Our Healthy Living Newsletter Thanks for signing up! Sign up for more FREE Everyday Health newsletters . Oops! Please enter a valid email address Submit We respect your privacy . Most of us take our teeth for granted … until something goes wrong.

Our teeth help us chew and digest food, play an important role in speech, and impact our health overall. And by brushing up on your dental health knowledge, you’ll be taking the first step toward giving your teeth the attention they deserve. How much do you know about your pearly whites? The Development of Teeth Humans have two sets of teeth, primary (or baby) teeth and then permanent teeth, which develop in stages. Although the timing is different, the development of each of these sets of teeth is similar. Here are some facts about how people develop teeth: Teeth tend to erupt in parallel, meaning that the top molar on your left side should grow in at about the same time as the top molar on the right. Tooth development begins long before your first tooth becomes visible. For example, a baby’s first tooth appears at around six months of age, but development of those teeth actually begins during the early second trimester of pregnancy. The crown of a tooth forms first, while the roots continue to develop even after the tooth has erupted. The 20 primary teeth are in place by age 3 and remain until around 6 years of age when they begin to fall out to make way for the permanent set of teeth.

Adult teeth start to grow in between 6 and 12 years of age. Most adults have 32 permanent teeth. Permanent teeth are larger and take longer to grow in than primary teeth. The Parts of the Tooth A tooth is divided into two basic parts: the crown, which is the visible, white part of the tooth, and the root, which you can’t see. The root extends below the gum line and anchors the tooth into the bone. Your teeth contain four kinds of tissue and each does a different job. These include: Enamel. Enamel is the visible substance that covers the tooth crown. Harder than bone, enamel protects the tooth from decay. Enamel is made up of phosphorous and calcium. Dentin. Underneath the enamel you find dentin, which is calcified and looks similar to bone. Dentin is not quite as hard as enamel, so it is at greater risk for decay should the enamel wear away. Cementum. This tissue covers the tooth root and helps anchor it (cement it) into the bone. It is softer than enamel and dentin; the best way to protect this softer tissue from decay is by taking good care of your gums.

Cementum has a light yellow color and is usually covered by the gums. But with inadequate dental care, the gums may become diseased and shrink, exposing the cementum to harmful plaque and bacteria. Pulp. Pulp is found at the center of your tooth and contains the blood vessels, nerves, and other soft tissues that deliver nutrients and signals to your teeth. Types of Teeth and What They Do Teeth help you chew your food, making it easier to digest. Each type of tooth has a slightly different shape and performs a different job. Types of teeth include: Incisors. Incisors are the eight teeth in the front and center of your mouth (four on top and four on bottom). These are the teeth that you use to take bites of your food. Incisors are usually the first teeth to erupt, at around 6 months of age for your first set of teeth, and between 6 and 8 years of age for your adult set. Canines. Your four canines are the next type of teeth to develop. These are your sharpest teeth and are used for ripping and tearing food apart.

Primary canines generally appear between 16 and 20 months of age with the upper canines coming in just ahead of the lower canines. In permanent teeth, the order is reversed. Lower canines erupt around age 9 with the uppers arriving between 11 and 12 years of age. Premolars. Premolars, or bicuspids, are used for chewing and grinding food. You have four premolars on each side of your mouth, two on the upper and two on the lower jaw. The first premolars appear around age 10 and the second premolars arrive about a year later. Molars. Primary molars are also used for chewing and grinding food. These appear between 12 and 15 months of age. These molars, also known as decidious molars, are replaced by the first and second permanent premolars (four upper and four lower). The permanent molars do not replace, but come in behind the primary teeth. The first molars erupt around 6 years of age (before the primary molars fall out) while the second molars come in between 11 and 13 years of age. Third molars. Third molars are commonly known as wisdom teeth.

These are the last teeth to develop and do not typically erupt until age 18 to 20, and some people never develop third molars at all. For those who do, these molars may cause crowding and need to be removed. Your mouth is important. Don’t take your teeth or oral health for granted. For good dental health, brush and floss your teeth regularly, don't smoke , eat a healthy diet, and see your dentist regularly for dental cleanings and checkups. A healthy mouth makes for a healthy body ... and a pretty smile. Last Updated: How Many Teeth Do We Have | Colgate® Oral Care How Many Teeth Do We Have? by Tina Callison by Tina Callison How many teeth do we have? Have you ever wondered that? Well, the answer depends on a few factors, the biggest factor being age. Children and adults have different sets of teeth. So, how many teeth do children have? Baby Teeth Children begin teething around six months of age. The technical term for these early teeth is deciduous teeth, because they eventually fall out, just as leaves fall of from deciduous trees in autumn. Most people know these teeth as baby teeth, though they are also sometimes called milk teeth or primary teeth.

In all, children have 20 baby teeth - 10 on the top and 10 on the bottom. These teeth act as placeholders for the adult teeth that grow in after the baby teeth fall out. Keep in mind that just because these teeth are destined to fall out, doesn't mean that they shouldn't be cared for the same way that adult teeth are cared for. Developing healthy eating and brushing habits should begin shortly after your child begins teething. At about age six most children begin to lose their baby teeth , which are then replaced with adult teeth. This process will continue into their early teens. Adult Teeth Adults have more teeth than children; most adults have 32 teeth. Among these teeth are 8 incisors, 4 canines, 8 premolars, and 12 molars (including 4 wisdom teeth). Most people have a complete set of adult teeth by the time they reach their teenage years. It is common for adults to have their wisdom teeth removed because there is not always enough room for them to grow in comfortably or without causing misalignment of other teeth. So, how many teeth do we have?

Typically, children have 20 and adults have 32 (28 if the wisdom teeth are removed). And each one of them needs your care. Learn more about taking care of your teeth here in the Colgate Oral Care resources. Related: MOUTH & TEETH ANATOMY Overview While the mouth is a small part of our overall anatomy, it’s filled with many parts and players, all of which work together to help you eat, drink, speak and have a radiant smile. The key players are incisors, canines, premolars, molars, crowns, gum line, root, enamel, dentin and pulp. What Are the Different Types of Teeth Here’s a quick overview of the different types of teeth in an average mouth: Incisors – the sharp, chisel-shaped front teeth (four upper, four lower) used for cutting food. Canines – sometimes called cuspids, these teeth are shaped like points (cusps) and are used for tearing and grasping food. Premolars – these teeth have two pointed cusps on their biting surface and are sometimes referred to as bicuspids. The premolars are for crushing and tearing food.

Molars – used for grinding and chewing food, these teeth have several cusps on the biting surface to help in this process. More videos you may like Kids Weigh in on the Ideal Amount of Time to Brush Their Teeth (0:55) What Are The Different Parts Of A Tooth? Each tooth has several distinct parts; here is an overview of each part: Enamel – this is the outer and hardest part of the tooth that has the most mineralized tissue in the body. It can be damaged by decay if teeth are not cared for properly. Dentin – this is the layer of the tooth under the enamel. If decay makes it through the enamel, it next attacks the dentin — where millions of tiny tubes lead directly to the dental pulp. Pulp – this is the soft tissue found in the center of all teeth, where the nerve tissue and blood vessels are located. If tooth decay reaches the pulp, you usually feel pain and may require a root canal procedure. Connect with us The Teeth (Human Anatomy): Diagram, Names, Number, and Conditions Next The teeth are the hardest substances in the human body. Besides being essential for chewing, the teeth play an important role in speech.

Parts of the teeth include: • Enamel: The hardest, white outer part of the tooth . Enamel is mostly made of calcium phosphate, a rock-hard mineral. • Dentin: A layer underlying the enamel. Dentin is made of living cells, which secrete a hard mineral substance. • Pulp: The softer, living inner structure of teeth. Blood vessels and nerves run through the pulp of the teeth. • Cementum: A layer of connective tissue that binds the roots of the teeth firmly to the gums and jawbone. • Periodontal ligament: Tissue that helps hold the teeth tightly against the jaw. A normal adult mouth has 32 teeth, which (except for wisdom teeth ) have erupted by about age 13: • Incisors (8 total): The middlemost four teeth on the upper and lower jaws. • Canines (4 total): The pointed teeth just outside the incisors. • Premolars (8 total): Teeth between the canines and molars. • Molars (8 total): Flat teeth in the rear of the mouth , best at grinding food.

• Wisdom teeth or third molars (4 total): These teeth erupt at around age 18, but are often surgically removed to prevent displacement of other teeth. The crown of each tooth projects into the mouth . The root of each tooth descends below the gum line, into the jaw. Teeth Conditions Cavities (caries): Bacteria evade removal by brushing and saliva and damage the enamel and deeper structures of teeth. Most cavities occur on molars and premolars. Tooth decay : A general name for disease of the teeth, including cavities and caries. Periodontitis : Inflammation of the deeper structures of the teeth (periodontal ligament, jawbone, and cementum). Poor oral hygiene is usually to blame. Gingivitis : Inflammation of the surface portion of the gums, around and between the crowns of the teeth. Plaque and tartar buildup can lead to gingivitis . Plaque : A sticky, colorless film made of bacteria and the substances they secrete. Plaque develops quickly on teeth after eating sugary food, but can be easily brushed off. Tartar : If plaque is not removed, it mixes with minerals to become tartar, a harder substance.

Tartar requires professional cleaning for removal. Overbite : The upper teeth protrude significantly over the lower teeth. Underbite : The lower teeth protrude significantly past the upper teeth. Rinsing teeth : Rinsing daily with an antiseptic mouthwash kills bacteria that cause bad breath and gum disease . Teeth cleaning : Professional teeth cleaning every six months may help prevent teeth and gum disease. Tooth filling : Drilling out the diseased part of a tooth and packing the space with a mineral filling can prevent a cavity from destroying the tooth. Root canal : The deep pulp of a tooth is drilled out, cleaned, and filled. A root canal is done when damage to the teeth has affected the deep pulp. Tooth extraction : If a tooth is too damaged to repair with a filling or root canal, it may be removed. Wisdom teeth are often extracted to prevent displacement of the other teeth. Braces : An artificial device or system that places teeth under tension for a long period of time. Eventually, braces can help crooked teeth become realigned. Mouth guard : A plastic mouthpiece can provide protection from teeth grinding and injury during sports.

Dental sealants : A plastic sealant applied to the teeth can help block bacteria from hiding in crevices on teeth surfaces. Sealants can help prevent cavities. Teeth whitening : Over-the-counter and professional chemical treatments can bleach teeth to a brighter white. Tooth sensitivity is the most common side effect. WebMD Image Collection Reviewed by William Blahd, MD on October 22, 2015 Sources Human Teeth vs. Animal Teeth Posted on 08/27/2013 · Posted in Health Information from Affiliated Dentists , Information Human Teeth vs. Animal Teeth We’ve written a lot about our teeth in past blogs, but how do our human teeth differ from animal teeth? What are the reasons they are different? Different Types of Animals To understand why there are different types of animal teeth but only one kind for humans, you must first know a little about the main four types of animals. Mammals A mammal is a warm-blooded animal. They are called vertebrates (backboned animals), have skin and hair covering their bodies, and they feed their young on mother’s milk after live birth. Humans are in this classification, and so are many other fascinating creatures around the world.

In fact, when the majority of people hear the word “animal” they immediately think of an animal that is a mammal. Birds Birds are also warm-blooded, but their bodies are covered in feathers instead of fur. Birds lay eggs from which their young hatch out of after a period of time. Birds have beaks and also have wings, and most – but not all – can fly. Reptiles Reptiles are also called vertebrates but they are cold-blooded instead of warm blooded like mammals. They have scales, shields or plates covering their bodies, and lay eggs (although a few do form the eggs themselves inside their own body until they hatch). Fish Instead of limbs and lungs, fish have fins and gills. Unlike the above animals, fish live underwater. Almost all fish cannot live outside of water, but there are a couple that can. Different Animals Mean Different Teeth The basic concept of teeth – to break down food for consumption – is the same for all humans. However, all humans have the same kinds of teeth, whereas animal teeth can vary depending on the animal’s classification (above) and diet. Herbivores An herbivore is an animal that gets energy from eating plants.

Their digestive system lets them digest almost all types of plants, including grass and leaves, but not meat. They typically eat all day long as they require a lot of energy to stay alive and well, which is why you see them grazing all the time. Herbivore Teeth Herbivores have more molars than we do. They use these flat teeth for grinding branches, grasses and seeds. Since their food doesn’t try to escape, they use their front teeth like pruning shears to clip leaves and stems. Carnivores These are animals that eat the meat and flesh of other living creatures. They have to hunt and kill their own food, and their digestive system lacks the ability to efficiently digest plant matter. Carnivore Teeth These types of animal teeth are very sharp and scissor-like. Their front teeth are used to bite and hold onto prey while their long canine teeth are used for tearing flesh and meat. Their molars are also sharp, and used for slicing rather than chewing because they mainly swallow their food in whole chunks. Omnivores This type of animal eats both plants and other animals. We humans are omnivores. Some hunt their food whereas others scavenge for it.

Omnivores typically can’t eat certain types of grains or plants, such as grass or leaves, but can eat fruits and vegetables. Even some insects are omnivores. Omnivore Teeth Again omnivores – us included! – eat a combination of plants and meat, so not surprisingly, they have a combination of sharp front teeth and grinding back molars. These types of animal teeth are set up like this whether we eat meat or not. The best way to see an example of this set of teeth is to look in a mirror and open wide! So What Makes Our Teeth Different? As you now know, humans are omnivores. However, this doesn’t mean our teeth are the same as other omnivores, such as most bears, pigs, opossums, piranhas (yes, really!), dolphins, raccoons … the list goes on and on ! There are many differences between human teeth and other animal teeth: Humans only get 2 sets of teeth in their lifetimes, whereas some animals like dolphins only get one, and some animals such as sharks grow multiple sets throughout their lives. Humans have at most 32 teeth, but many animals have way more than we do.

A horse can have up to 44, a dolphin can have up to 250, and a snail can have more than 25,000! Humans use their teeth for breaking down food, which animals do as well, but they also need their teeth for other forms of survival such as hunting, attacking and defending themselves. One of the best ways to see the differences between animal teeth and human teeth is to look at tooth charts of each. Human Teeth Charting If you’ve ever had a tooth that needed work, you might have heard your dentist refer to that tooth using a number. Each one of your teeth has a number. Using a full set of teeth (meaning wisdom teeth included), the numbering starts at the upper right wisdom tooth. This tooth is #1. It continues around the entire top arch, with your top middle teeth being #8 and #9, and ends on the upper left wisdom tooth as #16. Then it’s on to the bottom teeth, starting with the lower left wisdom tooth as #17 and working around the lower arch to finally come to a stop at the lower right wisdom tooth, #32.

If you have had your wisdom teeth extracted, these numbers do not change, meaning the last molar on the upper right is still considered #2. The majority of dental clinics use a visual chart such as the one below. This charting is the same for all adult permanent teeth (for children, letters are used for their baby teeth). Animal teeth, depending on their diet and classification, have different types of charting. These are used to identify what animal a skull came from. U is upper jaw and L is lower, and this chart goes front teeth (right side of chart) to back (left side of chart) on only ONE side of the mouth. Here is a human: BBC Science & Nature - Human Body and Mind - Skeleton Layer Food processing: Teeth cut through and chew up food, preparing it for digestion Enamel: Is the hardest substance in the human body Tooth decay: Bacteria in your mouth produce acid which rots your teeth Teeth break down food Your teeth prepare food for digestion by breaking it down and chewing it up. They do this by cutting, tearing, crushing and grinding: Your eight flat front teeth are good for biting, scraping and cutting.

They are called incisors Your four cone shaped canines are good at piercing and tearing food The teeth that crush and grind your food are your eight blunt premolars and your twelve broader, larger molars Hard teeth have a soft centre Your teeth are covered in enamel, which is the hardest substance in your body. It covers the exposed part of your teeth above your gum. The roots of your teeth are fixed into a socket in your jawbone. Although your teeth are hard on the outside, they actually have a soft centre. Inside your teeth is a cavity filled with pulp. Pulp is made up of connective tissue, blood vessels, and nerve fibres. It supplies nutrients to your teeth. The pulp cavity extends into the root of your teeth, forming the root canal. Two sets of teeth The first set of teeth known as deciduous or milk teeth erupts through the gums between eight months and three years of age. Milk teeth become loose and start to fall out as permanent teeth push through the gums at about six years of age. A full set of 32 permanent teeth is complete when wisdom teeth appear in the late teens or early twenties. The reason you have two sets of teeth probably comes down to size.

A full set of permanent teeth would be too big to fit into a young child's mouth. So milk teeth act as a bridge until the jaw is large enough to accommodate a full set of permanent teeth. Wisdom teeth The last teeth that emerge are your wisdom teeth. It's not clear what their function is, but some experts believe they're a remnant from a time when our ancestors had a more rugged diet and, as a result, longer, larger jaws. Now our jaws are smaller, there often isn't enough room for them, which is why wisdom teeth can cause problems. Tooth decay There are bacteria in your mouth that multiply when you eat sweet food. As these bacteria feed on food stuck on your teeth, they produce acid. This acid can dissolve enamel and eat through a tooth, right down to the nerve in its pulp cavity. A hole in a tooth like this provides a route for bacteria in your mouth to cause nasty infections in the root of a tooth. This can result in excruciating toothache. Retained Deciduous Teeth (Baby Teeth) in Cats | VCA Animal Hospital Retained Deciduous Teeth (Baby Teeth) in Cats By Jan Bellows, DVM, Dipl.

AVDC, ABVP Care & Wellness, Surgical Conditions March 12, 2010 How many sets of teeth do cats have? Like humans, cats have two sets of teeth in their lives. There are 26 deciduous teeth, also known as their primary, baby, milk, or kitten teeth, and 30 permanent teeth, also known as their adult teeth. When do kittens get their deciduous teeth? Kittens are born without any visible teeth. The deciduous teeth start erupting through the gums around three weeks of age and are normally finished erupting by four months of age. The kitten will have 26 primary teeth in all. A healthy mouth depends on healthy teeth. The ideal time to begin brushing a kitten’s teeth is when you first bring him home, before the discomfort of teething begins. Your veterinary health care team can help you determine the best products and methods of dental care for your kitten. "The ideal time to begin brushing a kitten's teeth is when you first bring him home, before the discomfort of teething begins." When do kittens get their permanent teeth? In kittens, the entire teething process is relatively rapid.

Teething begins in kittens at about 3½ to 4 months of age, when the primary incisors begin to be replaced by permanent incisors. By the time the average kitten reaches 6- 7 months of age, all 30 adult teeth will have erupted. What happens during teething? Long before adult teeth erupt through the gums, they begin developing from tooth buds located in the upper and lower jaws. As the adult teeth develop and get bigger, they begin to press against the roots of the baby teeth, stimulating the kitten’s body to begin resorbing the tooth roots. The baby tooth roots then weaken and finally disappear, leaving only the crowns behind. As the adult teeth push through the gums, the crowns of the baby teeth fall out. You may even find these hollow shells of teeth on the floor or in your kitten’s bedding, but more often than not the teeth will fall out while the kitten is eating and he will swallow them with the rest of his food. During the teething process, your kitten may drool, be reluctant to eat at times, and he may be irritable due to a tender mouth. Almost all kittens will have the urge to chew when they are teething.

It is important that you do what you can to direct your kitten’s chewing towards acceptable objects and don't allow any chewing of people's shoes, clothes, or furniture. Avoid hard objects as they can damage the teeth. You may also notice a characteristic breath odor, which is associated with teething. This odor is normal and will last as long as the kitten is teething. "During the teething process, your kitten may drool, be reluctant to eat at times, and he may be irritable due to a tender mouth. Almost all kittens will have the urge to chew when they are teething." What is a retained tooth? A retained tooth occurs when the tooth root is either incompletely resorbed or it did not resorb at all. When this happens, the baby tooth occupies the place in the mouth that is meant for the permanent tooth, forcing the permanent tooth to erupt at an abnormal angle or in an abnormal position. The end result is often crowding or malposition of the tooth, causing an abnormal bite. "A retained tooth is a deciduous or babytooth that is still present in the mouth after its replacement permanent or adult tooth has erupted." Which deciduous teeth are more commonly retained?

The most common teeth to be retained are the upper canine teeth, followed by the lower canine teeth and the incisors. However, in some cases, the premolar teeth may also be retained. What problems are caused by retained teeth? If both a deciduous tooth and a permanent tooth are in the same socket in the jaw, the crowding of the two teeth will increase the likelihood that food and debris will become trapped between the teeth. This can lead to problems such as tartar deposits, tooth decay, gingivitis and periodontitis, all of which can lead to premature loss of teeth. If the root of the retained tooth has only been partly resorbed, it can become badly infected. If teeth are malpositioned, they can rub against other teeth, wearing away the enamel and weakening the tooth. Occasionally, a retained deciduous tooth can cause a dental interlock which may interfere with the normal growth and development of the jaw bones. If the retained tooth is a lower canine, the permanent lower canine is forced to grow on the inside of the lower jaw and its tip usually grows towards the roof of the mouth, causing pain and damage which makes it difficult for your cat to eat.

"This can lead to problems such as tartar deposits, tooth decay, gingivitis and periodontitis, all of which can lead to premature loss of teeth." When and how are retained teeth treated? No two teeth should be in the same socket at the same time. If you notice a retained tooth in your kitten's mouth, make an immediate appointment for an examination. Unless the baby tooth is very mobile, extraction is the treatment of choice. Early extraction in these cases will usually allow the adult teeth to move into their proper positions. Once a diagnosis and treatment plan is discussed, the extraction should be scheduled as soon as possible. There is no reason to wait until your cat gets neutered or spayed. Extraction of the retained tooth will require a general anesthesia. Your veterinarian will take special care during the extraction of any retained tooth to avoid damaging the immature roots of the new permanent tooth. "Early extraction in these cases will usually allow the adult teeth to move into their proper positions." What happens if there is a delay before the retained tooth is extracted? If the retained primary tooth is not extracted in a timely manner, it is unlikely that the adult teeth will be able to move into their proper positions without orthodontic treatment.

In these cases, or for kittens with severe malocclusion problems, it may be necessary to selectively extract other teeth or to refer your cat to a veterinary dental specialist ( ) for orthodontic treatment to reposition the teeth. This treatment often includes the use of orthodontic buttons and elastics. Is there anything else I should know? In addition to regular tooth brushing, it is important to check your kitten's mouth every week until about seven to eight months of age to ensure that his teeth are growing normally. If you find any retained teeth, or if you suspect your kitten has an abnormal bite, bring him to your veterinary clinic immediately for an oral examination. This client information sheet is based on material written by: Jan Bellows, DVM, Dipl. AVDC, ABVP © Copyright 2013 LifeLearn Inc. Used and/or modified with permission under license. Rat Teeth Rat Teeth Rat molars Introduction to rat teeth Mammals have four kinds of teeth, that differ in shape, function, position in the mouth, and whether or not they are replaced. The four types are incisors, canines, premolars, and molars. Figure 1.

Drawing of a rat skull, showing the placement of the molars, incisors and diastema. © anne_rats Rats have incisors and molars (Fig 1). Incisors are the frontmost teeth in mammals. In rats, these are the four, long, sharp front teeth, two on top and two on the bottom. Rat incisors are highly specialized for gnawing. They are open-rooted, which means they grow throughout life. Molars are the rearmost teeth in the mouth, used for grinding food prior to swallowing it. Rats have 12 molars, six on the top and six on the bottom (and three on each side of each jaw). Molars are never replaced. Rats have only one set of teeth during their life (called monophyodont). Rats do not have canines (the conical, pointed teeth used for holding prey, defense, and combat), or premolars (grinding teeth behind the canines and in front of the molars). The rats have a long, toothless space in their mouth where the second incisors, canines and premolars would be. This space is called the diastema.

The number of different types of teeth in a species is described with a dental formula, which is written as: I n/n C n/n P n/n M n/n where I, C, P and M refer to the incisors, canines, premolars and molars respectively, and n/n refers to the number of upper and lower teeth of each type found on one side of the mouth. So, the rat's dental formula is: I 1-1, C 0-0, P 0-0, M 3-3. Rats have 8 teeth on the lower jaw and 8 on the upper, a total of sixteen teeth. Anatomy of a tooth Figure 2. Cross section of a mammalian molar. © anne_rats Teeth have the same composition as bone. A tooth consists of three layers of mineralized tissues: a hard external layer of enamel forms the crown of the tooth, a hard layer of cementum covers the root. The enamel and cementum surround a layer of softer, living dentin which makes up the bulk of the tooth. Dentin surrounds a soft core of pulp which contains blood vessels and nerves.

The periodontal ligament (also called the periodontal membrane) is a fleshy layer that lies between the tooth and the tooth socket. It holds the tooth in place, attaches it to its neighbors, and enables the tooth to resist the stress of chewing (Fig 2). Rat molars are similar to the molar depicted in Figure 2. Rat incisors, however, have a single, open, root that continues to grow throughout the rat's life. Rat incisors Figure 3. A rat's incisors The rat's incisors are the four long frontmost teeth in the rat's mouth (Fig 3). The upper incisors are shorter and yellower than the lower ones. The upper incisors are about 4 mm long and 1.5 mm wide, the lower ones are about 7 mm long and 1.2 mm wide (Weijs 1975). Incisors are specialized for gnawing . The rat's incisors are open-rooted (Fig 4), which means they grow throughout life (Addison and Appleton 1915).

If allowed to grow without restraint, the rat's incisors would grow in a spiral with an angle of 86º (Herzberg and Schour 1941). Rats spend their lives gnawing and wearing their teeth down, so the constant growth of their incisors prevents them from wearing their teeth away. Figure 4. Diagram of a rat skull with part of the bony alveoli removed to show the entire length of the incisors (adapted from Addison and Appleton 1915). Rat incisors erupt out of the gum 8-10 days after birth (Addison and Appleton 1915, Schour and Massler 1949). The eruption rate (the rate of growth) of the rat's incisors is very high: the adult rat's upper incisors grow on average about 2.2 mm per week (0.31-0.32 mm per day), and the lower incisors grow about 2.8 mm per week (0.4 mm per day) (Addison and Appleton 1915).

It takes about 40-50 days for new tooth generated at the base to reach the tip. The entire tooth is therefore never more than 40-50 days old (Schour and Massler 1942). This rapid growth also keeps the rats' incisors from getting cavities: any cavity would rapidly grow out and be worn away. The rate of incisor growth varies under different circumstances. If the incisors are trimmed, they grow faster, 1.0 mm per day (+/- 0.1 mm) (Law et al. 2003), so if a rat tends to gnaw on hard substances and thus wear its incisors away quickly, the incisors will grow faster to compensate. Individual incisors can grow at different rates depending on its length and that of its neighbor: if one incisor is shortened, it will grow back faster than the others (Burn-Murdoch 1999). If the upper and lower incisors do not meet properly (called a malocclusion), they cannot be worn away normally and become overgrown. Figure 5. Cross section of a rat's incisor halfway between the gum and the tip of the tooth.

Adapted from Addison and Appleton 1915. The incisors are colored with a yellowish pigment. The incisors start out white in the young rat, but by age 21 days the uppers have a slight yellow tinge. By 25 days the uppers are distinctly yellow and the lower incisors have acquired a little yellow. By 38 days these colors are more intense, with the uppers having more color than the lowers. The relationship between more pigmented upper incisors and less pigmented lower incisors remains true throughout the rat's life. In adult rats, the uppers are dark yellow-orange and the lowers are yellow (Addison and Appleton 1915). A cross-section of a rat's incisor shows three layers: An inner core of pulp, a surrounding layer of soft dentin, and a layer of hard enamel that covers only the front surface of the tooth (Fig 5, 6). The pulp cavity in the center of the tooth becomes narrower and narrower toward the tip of the incisor (Fig 5).

The pulp cavity reaches nearly to the end of the tooth, but at the very end it is filled in with hard material (granular osteodentine), so the sensitive pulp cavity is never actually exposed (Addison and Appleton 1915). Incisors are kept sharp by gnawing and bruxing , also called thegosis. Because rat incisors have hard enamel only on the front surface, the incisors wear at an angle, with the soft dentin in the back back wearing off before the enamel in the front. This guarantees a sharp, bevel-shaped cutting edge (Fig 6). Rats can actually move their lower jaw so far foward that their lower incisors are in front in front of their upper incisors. When a rat bruxes, its jaw is pulled forward, and its lower incisors sometimes grind behind the upper incisors (wearing down the uppers) and sometimes in front of them (wearing down the lowers) (Fig 7). Figure 6. Incisors have hard enamel on the front and soft dentin on the back. The dentin wears away first, leaving a sharp edge. Figure 7.

The lower incisors positioned behind (left) and in front of the upper incisors (right). Adapted from Schour and Massler 1942. Rats can gnaw powerfully, because the attachment points of the muscles that move the lower jaw up and down are far forward on the nose (Fig 8). This arrangement enables the rat to gnaw very effectively and forcefully. (One of these jaw muscles runs through the eye socket, behind the eyeball. This is why a rat's eyes vibrate in and out, called " eye-boggling ," when he bruxes enthusiastically). Figure 8. Rat skull, showing the forward placement of the attachment points of the masseter muscle on the upper jap. The medial masseter muscle passes through the eye socket, right next to the eye, and attaches on the muzzle. This is the muscle that "boggles" the eye when the rat bruxes. The lateral masseter muscle attaches just below and in front of the zygomatic arch. This muscle arrangement enables the rat to pull its lower jaw forward powerfully during gnawing.

When a rat gnaws, its lower jaw shifts forward, bringing the incisors into contact with each other and the molars out of contact with each other. The upper incisors hold the object, and the lower incisors cut against it. Hence, only the incisors are involved in gnawing -- molars do not touch each other when a rat gnaws. The enamel of rat incisors is hard, harder than iron, platinum and copper. Specifically, measured on Mohs hardness scale , the rat's lower incisors rank 5.5 (diamond is a 10). Human enemel is not quite this hard, measuring 5 on the Mohs hardness scale ( ref ). Figure 9. Photo showing skin flap and separation of the rat's lower incisors The rat has small flaps of cheek tissue on either side of the inside of the mouth that close behind the incisors, protruding into the gap between the incisors and the molars (the diastema) (Fig 9).

These flaps are believed to form a plug that keeps unwanted debris from entering the mouth (Addison and Appleton 1915, Olds and Olds, 1979; Bivin et al. 1979). Figure 10. Front of the lower jaw and incisors, showing the incisors closed (left) and open (right). The joint between the two halves of the lower jaw (mandibular symphysis, or symphysis mentis) is not fused, but is formed of fibrous tissue -- fibrocartilage and intercrossing ligaments. This fibrous tissue allows each side of the lower jaw to rotate slightly along its long axis, thus separating the lower incisors (Fig 9, 10). The widest angle obtainable is about 40º. The ability to separate the lower incisors is important in mastication: as a rat gnaws and bites, it adjusts the separation of its lower incisors (Weijs 1975, Jolyet and Chaker 1875 as reported in Addison and Appleton 1915).

Rat molars The rat's molars are the 12 grinding teeth located at the back of the mouth. They are broad, flat, unpigmented teeth that grind food into a pulp prior to ingestion. When a rat chews , the jaw moves back such that the molars are in contact with each other but the incisors are not. Hence, only the molars are involved in chewing -- the incisors do not touch each other when a rat chews. Rats have three sets of molars (first, second and third molars). The first molar erupts on the 19th day after birth, the second on the 21st. After the second molar erupts, rats can be weaned. The third molar comes in two weeks later, at around 35-40th day. By age 6 weeks the rat has its complete set of teeth, and by 125 days molar growth slows greatly. After this the molars continue to grow and wear away, but at such a slow rate as to be almost indiscernable (Schour and Massler 1949). Further reading:

Question: In humans how many teeth are incisors?
Answer: EIGHT